1. Field of the Invention
The present invention relates to an assembled battery constituted by combining a plurality of secondary battery single cells, and specifically, to an assembled battery which is constituted by combining small-scale secondary cells, and can be publicly used as a battery for driving the motor of an electric vehicle or the like.
2. Description of the Related Art
In recent years, control of carbon dioxide emissions has been sought against a background of a growing environmental protection movement. In such circumstances, in order to promote the introduction of an electric vehicle (EV), a hybrid electric vehicle (HEV), and a fuel cell vehicle (FCV) in place of a vehicle using fossil fuels such as gasoline-powered vehicle, automobile companies have been developing the battery for the driving motor, which has a key for practical application thereof. In such an application, a rechargeable secondary battery is used. In applications requiring high output and high energy density, such as the motor drive battery of the EV, the HEV, or the FCV, in practice, a single large-scaled battery cannot be manufactured. Therefore, an assembled battery constituted by connecting a plurality of cells in series has been generally used.
However, in such a method, the capacity of each cell needs to be made very large, and a specialized production line needs to be provided for production. Particularly, in the assembled battery for the EV or the like requiring a large capacity, each cell is very heavy, so that the cells are difficult to handle.
It is conceived that a number of small-scaled cells, which are easy to handle (hereinafter-, referred to as a unit cell) are connected to be used in applications of the EV, the HEV, and the FCV. Alternatively, it is conceived when a lithium ion secondary battery of high output and high energy density is used as an assembled battery for vehicles for charge and discharge, an assembled battery, in which each group having a plurality of unit cells connected in parallel are connected in series, is used. Thus, an assembled battery obtains a voltage of 400 V as a whole. In order to make a 12 V or a 42 V battery for vehicles to have higher performance, a more compact size, and lower costs, utilization of a consumer lithium ion battery becomes favorable. As the unit cell constituting the assembled battery for vehicles requiring a high voltage, a bipolar lithium secondary battery is also favorable. A bipolar lithium secondary battery comprises a plurality of bipolar electrodes which each have a positive electrode formed on one surface of a collector and a negative electrode formed on the other surface, and a plurality of bipolar electrodes are layered in series with a solid polymer electrolyte interposed therebetween.
The assembled battery for the electric vehicle is always used in a state where vibration is applied thereto. Therefore, vibration resistance is required such that there occurs no defect of a structural breakdown such as a fracture of a collector and a fracture of a collector weld portion, a fracture of a connection tab for electrically connecting the unit cells, or the like.
As a conventional technology of the assembled battery having a plurality of unit cells connected with each other as described above, there is a technology described in Japanese Patent Application Laid-Open No. 11-273643.